The present invention relates to the diagnostic imaging systems and methods. It finds particular application in conjunction with the Positron Emission Tomography (PET) and Single Photon Emission Tomography (SPECT) systems and will be described with particular reference thereto. It will be appreciated that the invention may also be applicable to other imaging modalities.
Nuclear medicine imaging employs a source of radioactivity to image a patient. Typically, a radiopharmaceutical is injected into the patient. Radiopharmaceutical compounds contain a radioisotope that undergoes gamma-ray decay at a predictable rate and characteristic energy. One or more radiation detectors are placed adjacent to the patient to monitor and record emitted radiation. Sometimes, the detector is rotated or indexed around the patient to monitor the emitted radiation from a plurality of directions. Based on information such as detected position and energy, the radiopharmaceutical distribution in the body is determined and an image of the distribution is reconstructed to study the circulatory system, radiopharmaceutical uptake in selected organs or tissue, and the like.
Nuclear medicine imaging has been increasingly used in cancer imaging due to the success of the tracer [18F]-fluorodeoxyglucose (FDG). Focal areas of abnormally increased FDG uptake are typical for many types of cancer. The main areas of interest are the diagnosis, staging, and monitoring of response to the treatment. A metabolic change can be established by comparing uptake values from pre-treatment and post-treatment scans. The FDG-PET imaging is also important for therapy planning, e.g. for dose planning. For such applications, the accurate localization and quantization of metabolic activity is essential. Often, the PET images are combined with the CT images of the same anatomical region. Typically, after the registration, the images are manually evaluated for localization and quantization of metabolic activity. Although, the hot spots are typically easily identified in the PET images, marking and delineation of the hot spots, however, are tedious tasks which slow down the overall workflow.
Another important area of the PET/SPECT imaging is myocardial perfusion imaging, where uptake of a tracer substance that contains a suitable radionuclide, such as Tc-99m, indicates the health condition of cardiac regions. Typically, the transaxial images, reconstructed from projection data, are reoriented into short-axis images. Short-axis images, which are perpendicular to the long axis of the left ventricle (LV), allow standardization of display and interpretation of images, and also make it possible to present 3D information in 2D polar maps, which is the current standard for quantification.
Current methods for determining the long axis of the left ventricle are based on models. Typically, such methods require the initial identification of the heart and initial model placement, which is followed by a model fitting procedure. The heart is typically segmented based on a global threshold. However, since the separation of different regions and the occurrence of noise spots strongly depend on the threshold setting, this methodology is often inaccurate. Another problem with automated thresholding procedures is that other organs with a high intensity, e.g. liver, might be selected instead of the heart. On the other hand, if the threshold is set high, the connectedness of the heart regions might disappear for infarcted cases.
The accurate initial placement is crucial for the model fitting algorithms. Initial misalignments can lead to invalid model positions. Besides, some additional constraints, for example, the approximate area and the shape of the heart, need to be incorporated in order to successfully fit the model. These constraints are camera dependent, and the parameters need to be adjusted for different cameras.
The present application provides new and improved methods and apparatuses which overcome the above-referenced problems and others.